As a natural phenomenon, dust-haze can be caused by factors from three aspects.
Increase of horizontal calm wind. Recently, the friction coefficient of the ground has been increasing with higher and higher buildings as the city construction developing rapidly, leading to weakened wind when it is passing urban areas. More calm winds is to the disadvantage of the extension and dilution of atmospheric pollutants to the outer space of the city and make high concentration of pollution easier inside the city.
Vertical temperature inversion. The temperature inversion layer is like a pot cover above the city and creates temperature inversion that the temperature of upper air is higher than that of lower part. On the condition that the climate is normal when pollutants can move to upper colder air and be released to the atmosphere in this loop. However, when vertical temperature inversion happens, pollutant stays in the lower air because it is colder.
Increase of floating particles. As the industrial development went on and on these years, more and more motor vehicles appear and there were a great larger amount of released pollutants and floating particles in city. This is directly responsible for the low visibility, which put all the city under a gray cover.
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